Stage fuel combustion as an effective method to decrease metal losses in reheating furnaces

In the process of metal reheating before rolling, its losses as a result of high temperature oxidation (metal losses) reach 1–2%. At that the heat transfer for the flame jet to the metal decreases, which results in an increase of fuel consumption and increase of danger of surface defects formation. One of the ways to decrease metal losses in the form of scale during heating due to the organization of the stage burning of fuel considered. This principle implies creation of a neutral or reducing atmosphere of the furnace in the end zones in the direction of metal movement. This is achieved by supplying less amount of air to these zones than necessary for the complete combustion of the fuel. Afterburning of fuel occurs in the first zones of the furnace. Thus, the amount of air required for complete combustion of the fuel does not change and there is no increase in the formation of CO emissions. The technology implementation has been carried out on a reheating furnace equipped with instruments for monitoring the atmospheric composition along the entire furnace length. The values of the excess air factors were varied within the existing process schedule. The application of the stage mode on three walking beam furnaces of a wide-strip hot rolling mill made it possible to reduce metal losses to scale by an average of 9.3% (1.3 kg/t). At the same time, there were no cases of deterioration of other parameters of the heating process, such as fuel consumption, heating quality, formation of hard-to-remove scale.